The present invention relates to clutches and, more particularly, to a bi-directional electro-mechanical and electro-hydraulic overrunning clutch for providing four wheel drive capability with automatic backdrive.
In recent years there has been a tremendous demand for off-road and all terrain vehicles. The interest in these types of vehicles has led to a wide variety of innovations. Many of the innovations have centered around making the vehicle more adaptable to changing road conditions, e.g., dirt roads, pavement and gravel. As the road terrain changes, it is desirable to vary the driving capabilities of the vehicle to more efficiently navigate the new terrain. Prior four-wheel drive and all terrain vehicles were cumbersome since they required the operator to manually engage and disengage the secondary drive shaft, e.g., by stopping the vehicle to physically lock/unlock the wheel hubs. Improvements in vehicle drive trains, such as the development of automated systems for engaging and disengaging a driven axle, eliminated many of the problems of the prior designs. These automated drive systems are sometimes referred to as xe2x80x9con-the-flyxe2x80x9d four wheel drive. Many of these systems, however, require the vehicle to be in either 2-wheel or 4-wheel drive at all times.
Generally, all four-wheel drive vehicles include a differential for transferring torque from a drive shaft to the driven shafts that are attached to the wheels. Typically, the driven shafts (or half shafts) are independent of one another allowing differential action to occur when one wheel attempts to rotate at a different speed than the other, for example when the vehicle turns. The differential action also eliminates tire scrubbing, reduces transmission loads and reduces understeering during cornering (the tendency to go straight in a corner). There are four main types of conventional differentials: open, limited slip, locking, and center differentials. An open differential allows differential action between the half shafts but, when one wheel loses traction, all available torque is transferred to the wheel without traction resulting in the vehicle stopping.
A limited slip differential overcomes the problems with the open differential by transferring all torque to the wheel that is not slipping. Some of the more expensive limited slip differentials use sensors and hydraulic pressure to actuate clutch packs locking the two half shafts together. The benefits of these hydraulic (or viscous) units are often overshadowed by their cost, since they require expensive fluids and complex pumping systems. The heat generated in these systems, especially when used for prolonged periods of time, may also require the addition of an auxiliary fluid cooling source.
The third type of differential is a locking differential that uses clutches to lock the two half shafts together or incorporates a mechanical link connecting the two shafts. In these types of differentials, both wheels can transmit torque regardless of traction. The primary drawback to these types of differentials is that the two half shafts are no longer independent of each other. As such, the half shafts are either locked or unlocked to one another. This can result in problems during turning where the outside wheel tries to rotate faster than the inside wheel. Since the half shafts are locked together, one wheel must scrub. Another problem that occurs in locking differentials is twichiness when cornering due to the inability of the two shafts to turn at different speeds.
The final type of differential is a center differential. These types of differentials are used in the transfer case of a four wheel drive vehicle to develop a torque split between the front and rear drive shafts.
Many differentials on the market today use some form of an overrunning clutch to transmit torque when needed to a driven shaft. One successful use of an overrunning clutch in an all terrain vehicle is disclosed in U.S. Pat. No. 5,036,939. In that patent, the vehicle incorporates overrunning clutches where the wheel hub mounts to the axle, thus allowing each wheel to independently disengage when required.
Another successful use of an overrunning clutch in a differential is disclosed in U.S. Pat. No. 5,971,123, commonly owned by the assignee of the present invention. That patent describes an innovative electro-mechanical bi-directional overrunning clutch differential which addressed many of the problems inherent in the prior drive systems. The bi-directional overrunning clutch differential utilized electrically controlled coils to advance and retard a roll cage, thereby controlling the ability of the differential to engage and disengage depending on the operational state of the primary and secondary wheels. The bi-directional differential in U.S. Pat. No. 5,971,123 also describes a backdriving system. The backdriving system operates by controlling the energizing of selected coils to actively engage the secondary shafts in certain situations where extra traction is needed. For example, when the vehicle is driving down a slope the system engages the front wheels, which are the wheels with the better traction.
The backdrive system in the bi-directional differential disclosed in U.S. Pat. No. 5,971,123, like the overrunning clutch mechanism, uses coils to drag and advance the roll cage for engaging and disengaging the shafts.
While the electro-mechanical bi-directional differential in U.S. Pat. No. 5,971,123 provides a substantial improvement over prior differential drives, the design of the system did not readily permit automatic engagement of the backdrive.
A need, therefore, exists for an improved bi-directional differential which is compact, relatively inexpensive to manufacture and which provides automatic backdrive capability.
A bi-directional overrunning clutch is disclosed for controlling torque transmission between a secondary drive shaft and secondary driven shafts. The present invention, when used in a vehicle, provides four wheel drive capability in the event of traction loss on any primary drive shaft.
The overrunning clutch includes a differential housing with a pinion input shaft extending outwardly from the housing. One end of the pinion input shaft is engaged with the secondary drive shaft. The other end of the input shaft is located within the differential housing and includes an input gear. The input gear preferably engages with a ring gear rotatably disposed within the housing such that rotation of the input gear produces concomitant rotation of the ring gear.
A clutch housing is disposed on the ring gear and includes an inner surface. At least one and preferably two races are located adjacent to the inner surface. At least one of either the race or the inner surface defines a cam surface. Each race is engaged with an output hub. The output hub, in turn, is engaged with a secondary driven half shaft.
A roll cage is located between the race and the inner surface of the housing. The roll cage has a plurality of slots which are preferably spaced equidistantly about its circumference. Each slot has a roll located therein and which is biased by an independent spring. The roll cage is movable with respect to the clutch housing and the races.
An armature plate is located adjacent to and engaged with the roll cage so that the armature plate rotates in conjunction with the roll cage. The engagement between the armature plate and the roll cage furthermore permits the armature plate to be rotated with respect to the roll cage.
An indexing device, such as a driving coil is mounted within the differential housing adjacent the armature plate. The coil is adapted to produce an electromagnetic field when energized which hinders the rotation of the armature plate, thus causing the roll cage to drag with respect to the clutch housing. The dragging of the roll cage with respect to the clutch housing causes the rolls to engage the clutch housing and the race when the wheels on the primary drive shaft lose traction. When traction loss occurs, the rolls become wedged between the clutch housing and the race so as to provide torque transfer between the two.
A first clutch pack assembly is mounted to the clutch housing between the armature plate and the differential housing. The clutch pack assembly is similar to a slip clutch design. The clutch pack assembly includes a clutch pack housing which surrounds at least one friction plate and at least one drive plate. The friction plate and the drive plate are rotatable with respect to one another when the plates are not forced into contact with one another. The friction or wear plate is engaged with the clutch pack housing such that rotation of the clutch pack housing produces concomitant rotation of the friction plate. The drive plate is attached to the output hub such that the drive plate rotates in conjunction with the output hub. In one embodiment, the drive plate includes splines that engage with mating splines formed on an adapter ring. The adapter ring, in turn, is splined to the output hub.
The clutch pack assembly also includes a hydraulic piston which is mounted to the clutch pack housing and adapted, when actuated, to apply pressure to the friction plate and drive plate. When sufficient pressure is applied to the friction and drive plates, the output hub becomes engaged with the clutch pack housing and, as such, the clutch housing and the input pinion.
A second clutch pack assembly is preferably mounted to the clutch housing on the opposite of the clutch housing from the first clutch pack assembly. The second clutch pack assembly includes a second clutch pack housing which surrounds at least one friction plate and at least one drive plate. The friction plate and the drive plate in the second clutch pack assembly are rotatable with respect to one another when the plates are not forced into contact with one another. The friction plate is engaged with the second clutch pack housing such that rotation of the second clutch pack housing produces concomitant rotation of the friction plate. The drive plate is engaged to the output hub such that the drive plate rotates in conjunction with the output hub. In one embodiment, the drive plate is splined to an adapter ring which, in turn is splined to the output hub.
The second clutch pack assembly also includes a hydraulic piston which is mounted to the second clutch pack housing and adapted, when actuated, to apply pressure to the friction plate and drive plate. When sufficient pressure is applied to the friction and drive plates, the output hub becomes engaged with the second clutch pack housing and, accordingly, with the clutch housing and the input pinion.
The foregoing and other features and advantages of the present invention will become more apparent in light of the following detailed description of the preferred embodiments thereof, as illustrated in the accompanying figures.